1. Field of the Invention
The present invention relates to method and apparatus for controlling the Z-position of a probe used in a microprobe analyzer.
2. Description of Related Art
In some microprobe analyzers, a mechanical probe is brought into contact with the surface of a sample, and a tiny piece of the sample including a certain region of the substrate of the sample is separated and extracted using an ion beam and the probe, thus preparing the sample piece for microanalysis. Other microprobe analyzers are used to measure the characteristics of a sample while a voltage is applied to the surface of the sample with a probe. Such a microprobe analyzer is equipped with a Z-drive for bringing the probe into contact with the surface of the sample.
In a related art apparatus of this kind, information about the height of the probe from the surface of the sample is obtained based either on a secondary electron image in which a shadow produced immediately before the probe touches the sample surface is observed or on variations in the positional relationship between a probe image formed when the ion beam is made to obliquely hit the sample and an image of the sample (see, for example, JP2002-40107).
The above-described microprobe analyzer is equipped with a microscope mechanism for recognizing the portion of the sample to be observed and a portion of the sample with which the probe should be brought into contact. Since the image created by the microscope mechanism is a two-dimensional image, positions along the height cannot be recognized. Therefore, the operator causes the probe to descend toward the sample while observing the sample, thus bringing the probe into contact with the surface of the sample.
However, these manipulations impose excessive stress to the operator. Furthermore, the probe may be struck against the sample surface, damaging the probe. Such cumbersome manipulations and damage to the probe will eventually lead to a decrease in the throughput.
The probe is normally made of a hard metal, such as tungsten, and so if such a probe comes into contact with a semiconductor sample of Si or the like, a Schottky barrier is created in the probe. As a result, it becomes difficult to electrically connect the probe with the sample.